I've heard it was the 105, or the 180, but I also read a quote from him in which he was being evasive in a way that made it seem like he didn't really know for sure. It makes no real difference, because the shot speaks for itself and has for generations now, but it still would be an interesting piece of trivia to pin down.

He is currently exhibiting more than 100 large prints in Copenhagen, Denmark, and gave a talk at the opening. The Afghan girl was photographed inside a tent in rather dim light (1/60th or thereabouts). It is impressively sharp even at close-up inspection of the large print displayed at the exhibition considering this.